We have previously described the presence of catecholaminergic neurons expressing low affinity nerve growth factor receptors (NGFR) in the rhesus monkey ovary. We are now assessing the postnatal ontogeny of these NGFR-positive cells, as well as their catecholaminergic capabilities in ovaries from neonatal to senescent animals. Immunocytochemistry (ICC) for NGFR revealed that the greatest number of these neurons were present in neonatal ovaries, with the numbers gradually declining throughout postnatal life, so that these were only occasional neurons by 20 years of age. ICC for tyrosine hydroxylase (TH), revealed that the capability of the neurons to produce catecholamines was lowest in neonatal (2 mo) ovaries, then increased dramatically during juvenile (8 mo) and again during peripubertal (3.5 yr) development. Our most recent data, although preliminary, suggests that the number of TH-positive neurons decline gradually until approximately 12 years of age. Subsequently, the number of these neurons declined markedly by 17 years of age, becoming virtually absent in monkeys reaching 20-27 years of age. We have also initiated experiments to determine the origin and prenatal ontogeny of ovarian neurons. We have positively identified NGFR-neurons in monkey ovaries from fetuses as early as 100 days. Unfortunately, we have had difficulty in obtaining younger fetuses. We have, however, recently discovered the presence of NGFR/TH-positive neurons in adult pig ovaries, and are now collecting pig fetuses at various ages in order to continue the prenatal ontogeny study. To date, we have obtained evidence that the neurons (some of which are TH-positive) are migrating from the developing neural tube and are already within the genital ridge and the undifferentiated gonad by fetal day 23. Earlier ages are currently being collected.